This document describes a tunable capacitor, and more particularly to production of electrical components for electrical circuits, specifically for precision Radio Frequency (RF) applications.
A capacitor is a device for storing electrical energy. The amount of stored energy is defined as a capacitance of the capacitor, which is measured in units of Farads. Some capacitors can be tuned, i.e. having a variable capacitance, but adjustable to a particular capacitance. Such tunable capacitors are sometimes referred as variable capacitors, trimmer-capacitors, or simply “trimmers”.
Trimmers come in a variety of sizes and levels of precision. The capacitance of trimmers can be adjusted with a small screwdriver, in which several turns of an adjustment screw can reach a desired end value, allowing for some degree of accuracy. Conventional trimmers include two electrically conductive electrodes separated by a dielectric material, and the distance between the electrodes and/or dielectric material affects the capacitance. To tune a trimmer, the distance between the electrodes or overlapping area of the electrodes is changed, and results in changing the capacitor's capacitance. The following formula governs such changes:
                              C          =                                    ɛ              ·              S                        d                          ,                            (        1        )            
where                C—capacitance of the trimmer,        ∈—dielectric constant of dielectric,        S—overlapping area,        d—distance between the electrodes        
Conventional trimmers, however, are not very accurate, and have limited range of capacitance value. Further, they do not allow automatic digital control of the capacitance value with high accuracy, as is required for such applications as tunable RF filters.